title: Characterization of a major facilitator superfamily (MFS) tripartite efflux pump EmrCABsm from Stenotrophomonas maltophilia.
abstract: OBJECTIVE
  To characterize the emrRCABsm operon of Stenotrophomonas maltophilia.
  
  
  METHODS
  The presence of the emrRCABsm operon was verified by RT-PCR. The regulatory role of EmrRsm was investigated by ΔemrRsm mutant construction and promoter transcriptional fusion assay. A susceptibility test was employed to assess the substrate spectrum of the EmrCABsm efflux pump. The requirement for each component of the EmrCABsm pump was assessed by individual mutant construction and susceptibility testing. The expression of the emrRCABsm operon was evaluated by an induction assay, using different compounds as inducers.
  
  
  RESULTS
  emrRsm, emrCsm, emrAsm and emrBsm formed a four-member operon that was negatively regulated by the MarR-type transcriptional regulator EmrRsm. The emrRCABsm operon was intrinsically poorly expressed and the EmrCAB pump favoured extrusion of the uncoupling agents carbonyl cyanide 3-chlorophenylhydrazone (CCCP) and tetrachlorosalicylanilide (TCS), and the hydrophobic antibiotics nalidixic acid and erythromycin. However, the emrRCABsm operon could not be derepressed by CCCP, nalidixic acid, TCS, 2-chlorophenylhydrazine hydrochloride or salicylate, which are known to be possible inducers for MarR-type regulons. Each component of the EmrCABsm pump was apparently essential for pump function.
  
  
  CONCLUSIONS
  The EmrRsm-regulated EmrCABsm efflux pump is involved in the extrusion of hydrophobic compounds.
authors.affiliation: Department of Biotechnology and Laboratory Science in Medicine, National Yang-Ming University, Taipei 112, Taiwan.
authors.forename: Yi-Wei
authors.initials: YW
authors.lastname: Huang
authors.forename: Rouh-Mei
authors.initials: RM
authors.lastname: Hu
authors.forename: Fang-Yeh
authors.initials: FY
authors.lastname: Chu
authors.forename: Hui-Rung
authors.initials: HR
authors.lastname: Lin
authors.forename: Tsuey-Ching
authors.initials: TC
authors.lastname: Yang
mesh_terms: D018435:ATP Binding Cassette Transporter, Subfamily B / Q000235:genetics* / Q000378:metabolism*; D019677:Artificial Gene Fusion; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D017353:Gene Deletion; D017930:Genes, Reporter; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D026901:Membrane Transport Proteins / Q000235:genetics* / Q000378:metabolism*; D008826:Microbial Sensitivity Tests; D008969:Molecular Sequence Data; D009876:Operon; D009930:Organic Chemicals / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017422:Sequence Analysis, DNA; D020615:Stenotrophomonas maltophilia / Q000235:genetics* / Q000378:metabolism*
chemical_list: D018435:ATP Binding Cassette Transporter, Subfamily B; D004269:DNA, Bacterial; D026901:Membrane Transport Proteins; D009930:Organic Chemicals
keywords: antibiotic resistance; bacteria; efflux pump